Spiro[2.5]octane-5,7-dione is an important intermediate for the production of pharmaceutically active ingredients. The synthesis of this intermediate has been described in WO 2006/72362 and is quite complex, costly and unattractive for larger quantities. Therefore there is a need for a new synthesis route to manufacture spiro[2.5]octane-5,7-dione efficiently and in the high quality needed for pharmaceutical intermediates.